This invention relates to high-speed playback techniques in consumer digital video tape recorders (VTRs) for recording/reproducing digital video signal by rotating magnetic heads, and particularly to a tracking control method suitable for trick playback of magnetic tape on which information for trick playback at an arbitrary speed faster than normal playback speed is recorded dispersedly over the respective tracks as the rotary magnetic heads scan.
The video playback system of digital VTR has the so-called normal play mode in which the recorded video signal is reproduced at normal speed, and the fast playback mode including fast forward and fast reverse modes, or what is called the trick play mode in which particular pictures are fast searched for or in which video images are fast forwarded while being viewed. In the fast playback mode, three-times normal speed, nine-times normal speed or other playback speed can be set. The "trick playback" used in the specification of this application means such high-speed playback.
The consumer use digital VTR employs image compression technology in order to reduce the amount of data being recorded on magnetic tape. An example of the image compression technology used is generally the so-called MPEG (Moving Picture Experts Group) system.
In the MPEG system, since the video image is built up by use of the difference between adjacent frame data when the continuity of successive frame data is lost by the fast playback, video image cannot be decoded from this data.
A fast playback method in VTR using image compression by MPEG system is proposed which is disclosed in, for example, "FAST SCAN TECHNOLOGY FOR DIGITAL VIDEO TAPE RECORDERS", IEEE Transactions on Consumer Electronics, Vol. 39, No. 3, August 1993, pp. 186-191.
According to this method, in order that video images can be decoded even in the fast playback mode, video data for fast playback mode which is separated from the video data for normal playback is dispersedly recorded on a magnetic tape at particular positions along a scan path of the playback heads according to the tape speed for trick playback. Thus, trick playback such as searching and shuttle playback can be performed even from the tape on which compressed data recording is already made by MPEG algorithms.
In the trick playback according to the above method, however, there are the following problems.
Since the video data for trick playback is recorded only on particular tracks corresponding to a path along which the heads scan the magnetic tape, the rotary magnetic heads must be swiftly controlled to precisely trace a certain video-data-recorded track when playback speed is changed from normal speed to a trick play speed or from a trick play speed to another different trick play speed. In this method, any head-controlling mechanism is not considered and not disclosed.